Method and apparatus for cold working seamless tubes

ABSTRACT

A seamless tube is cold worked to decrease spiral internal variations by placing a floating mandrel within the tube to be worked and positioning the tube and mandrel within a die. The mandrel has a maximum external diameter substantially equal to the desired internal diameter of the finished tube and is initially positioned with its forward end within the die. The tube is then pulled through the die where its outer and inner diameters are reduced to sizes less than the outer and inner diameters of the finished tube. The initial movement of the tube causes the floating mandrel to move entirely through the die. Continued movement of the tube places the tube in tension and expands its inside diameter as it passes over the mandrel.

nited States Patent 1 [111 afiamee A Gunn June 12, 1973 METHOD AND APPARATUS FOR COLD WORKING SEAMLESS TUBES [75] Inventor: William J. Gunn, Gary, Ind.

[73] Assignee: United States Steel Corporation,

Pittsburgh, Pa.

[22] Filed: Nov. 17, 1970 [21] Appl. No.: 90,248

[52] 11.8. C1 72/283, 72/370 [51] Int. Cl. B21c 1/24 [58] Field of Search 72/274, 283, 370

[56] References Cited UNITED STATES PATENTS 2,258,242 10/1941 Ditzel 72/283 1,967,487 7/1934 Waisner 72/283 2,102,099 12/1937 Singer 72/283 2,234,863 3/1941 Heetkamp 72/283 1,685,636 9/1928 Kemp 72/479 Primary ExaminerCharles W. Lanham Assistant Examiner-M. J. Keenan Attorney-Donald S. Ferito A seamless tube is cold worked to decrease spiral internal variations by placing a floating mandrel within the tube to be worked and positioning the tube and mandrel within a die. The mandrel has a maximum external diameter substantially equal to the desired internal diameter of the finished tube and is initially positioned with its forward end within the die. The tube is then pulled through the die where its outer and inner diameters are reduced to sizes less than the outer and inner diameters of the finished tube. The initial movement of the tube causes the floating mandrel to move entirely through the die. Continued movement of the tube places the tube in tension and expands its inside diame- ABSTRACT ter as it passes over the mandrel.

3 Claims, 2 Drawing Figures PMENIED INVENTOR. WILL/AM J. GUN/V M Attorney 1 METHOD AND APPARATUS FOR COLD WORKING SEAMLESS TUBES This invention relates to a method and apparatus for cold working seamless tubes and more particularly to cold working seamless tubes to remove or decrease the spiral of wall variation in tubes to be used in the manufacture of hydraulic cylinders. The spiral of wall variation can cause a piston to bind or score the wall of the cylinder or cause the piston rod to bind or score when the cylinder is cycled. For this reason seamless tubes are not completely satisfactory for use as hydraulic cylinders unless they are machined. F itzmaurice U.S. Pat. No. 3,517,536 dated June 30, 1970, shows one method of doing this. Machining of the tube is a relatively expensive operation. It is also often necessary to subject the tube to a subsequent straightening operation.

' It is therefore an object of my invention to provide a relatively inexpensive method of eliminating or decreasing spiral internal variations in seamless tubes without removing metal therefrom.

Another object of my invention is to provide apparatus suitable for carrying out my method.

' Still another object is to provide such apparatus which can be produced by a relatively simple modification of conventional tube drawing equipment.

A further object is to provide such apparatus which produces a straight tube without a further straightening operation.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIG. 1 is an elevation, partly in section, of the apparatus of my invention; and

FIG. 2 is a view showing part of the apparatus of FIG. 1 on an enlarged scale. I

Referring more particularly to the drawings, reference numeral 2 indicates a tube drawing die. A mandrel 4 is supported in axial alignment with the die opening and its entry end is attached to one end of mandrel support 6. The other end of mandrel support 6 is attached to a holder 8. The holder 8 is adjustably mounted for movement toward and away from die 2, but is fixed during the drawing operation. The mandrel has a cylindrical intermediate portion 10 having a diameter substantially equal to the desired inside diameter of the finished tube, a cylindrical portion 12 of slightly less diameter extending away from the holder 8, and an end portion 14 extending from the intermediate portion 10 toward the holder 8 with a gradually reducing diameter. This may be tapered or curved, as shown. The mandrel support 6 includes a first rod 16 having one end attached to the holder 8 and the other end attached to cylinder 18. The other end of the cylinder 18 has an internal abutment 20 with a hole 22 therethrough for receiving a piston rod 24. One end of the piston rod 24 is attached to the mandrel 4 and the other end attached to a piston '26 which is slidably mounted within the cylinder 18. A draw chain 28 is located on the exit side of die 2 and is adapted to pull a hook 30 which is connected to a tube gripping device 32. All the parts described, except for the shape of the mandrel and the details of the mandrel support may be part of a conventional cold drawing equipment such as shown and described on Pages 859 and 860 of the Eighth Edition of The Making, Shaping and Treating of Steel" published by United States Steel Corporation.

In operation, a workpiece or tube T is provided which is preferably a cold drawn seamless tube, but may be a hot rolled seamless tube. In either case the tube T is preferably provided with a leading pointed end TP. In one particular example the tube T has a 5.580 inch outer diameter, a 4.780 inch inner diameter and a 0.400 inch wall thickness; the mandrel 4 has a length of 13 inches with the length of cylindrical portion 10 being four inches and the length of cylindrical portion 12 being eight inches; the diameter of the cylindrical portion 10 is 4.490 inches and the diameter of cylindrical portion 12 is 4.480 inches; the mandrel 4 is free to move a distance of 17-% inches; the inside diameter of the die 2 is 5.230 inches. The tube T is telescoped over the mandrel 4 in the usual manner and the assembly positioned within the die 2 also in the usual manner. For this purpose the conventional holder 8 may be moved away from the die 2 and may also be pivoted through a small angle. It will be seen that the forward end of the mandrel 4 is positioned within the die 2 as shown in FIG. 1. The tube is then gripped on the point TP by means of the gripping mechanism 32 and the hook 30 engaged with chain 28. It will be noted that the piston 26 is in its rearward position at this time. As the tube T is drawn through the die 2 as shown in FIG. 1 its outside diameter will be reduced to a size smaller than that desired in the finished tube. This size preferably is such as to permit an expansion of 1.3 percent to the finished size. The initial movement of the tube T also causes the floating mandrel 4 to move through the die 2 to a position completely on the exit side of the die as shown in FIG. 2. This distance is preferably 2-% inches so as to permit free unimpeded expansion of the tube over the mandrel. The length of the mandrel is important in that it acts as an internal guide and prevents wobbling during the tube drawing operation. As the tube expands over the mandrel 4 it is under tension due to its engagement with the die 2 and the mandrel 4. The finished tube has an outside diameter and a wall thickness less than that of the starting tube and a length longer than the original length. The operation is the combination of a normal draw pass, a sink pass and an expanding pass. The initial movement which pulls the mandrel through the die and places the mandrel in position ahead of the die reduces the tube diameter and wall as in a normal drawing pass for a distance equal to the length of the mandrel. As the expanding operation continues the remainder of the tube receives a sink pass as it is pulled through the die since it is not restrained by the mandrel. This reduces the outside diameter of the tube with no significant change in wall thickness. The mandrel 4 then expands the outside diameter of the tube the amount required to produce the internal surface required by the customer. That part of the tube worked before the mandrel 4 is positioned beyond the die 2 is cropped off. No further straightening operation is necessary because drawing of the tube over the mandrel under tension produces a straight cold worked tube even though the initial workpiece is not sufficiently straight for its intended purpose.

While one embodiment of my invention has been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. The method of cold working a seamless tube to decrease spiral internal variation which comprises providing a tube to be worked having outer and inner diameters greater than the outer and inner diameters desired in the finished tube, passing said tube to be worked through a die to reduce its outer and inner diameters to sizes less than the outer and inner diameters desired in the finished tube, positioning within the tube to be worked entirely on the exit side of said die a mandrel including a cylindrical intermediate portion of substantial length and a diameter substantially equal to the desired internal diameter of the finished tube, a forward cylindrical portion of substantial length extending from said intermediate portion having a diameter slightly less than the cylindrical intermediate portion and a rearward end portion extending from said intermediate portion with a gradually reducing diameter, and causing relative movement between the mandrel and tube to place the tube in tension and expand its inside diameter after it has passed through said die.

2. The method of claim 1 in which said relative movement is obtained by holding said mandrel stationary and pulling said tube through said die.

3. The method of claim 1 in which said relative movement is obtained by first positioning the tube to be worked within the die with its first end extending a short distance from the exit end of the die and its second end extending from the entry end of the die, positioning the mandrel within the tube with its leading end within the die and its trailing end on the entry end of the die, then gripping the first end of said tube, then pulling the tube longitudinally through the die and at the same time positioning the mandrel entirely on the exit side of said die, and continuing pulling of said tube until the operation is completed. 

1. The method of cold working a seamless tube to decrease spiral internal variation which comprises providing a tube to be worked having outer and inner diameters greater than the outer and inner diameters desired in the finished tube, passing said tube to be worked through a die to reduce its outer and inner diameters to sizes less than the outer and inner diameters desired in the finished tube, positioning within the tube to be worked entirely on the exit side of said die a mandrel including a cylindrical intermediate portion of substantial length and a diameter substantially equal to the desired internal diameter of the finished tube, a forward cylindrical portion of substantial length extending from said intermediate portion having a diameter slightly less than the cylindrical intermediate portion and a rearward end portion extending from said intermediate portion with a gradually reducing diameter, and causing relative movement between the mandrel and tube to place the tube in tension and expand its inside diameter after it has passed through said die.
 2. The method of claim 1 in which said relative movement is obtained by holding said mandrel stationary and pulling said tube through said die.
 3. The method of claim 1 in which said relative movement is obtained by first positioning the tube to be worked within the die with its first end extending a short distance from the exit end of the die and its second end extending from the entry end of the die, positioning the mandrel within the tube with its leading end within the die and its trailing end on the entry end of the die, then gripping the first end of said tube, then pulling the tube longitudinally through the die and at the same time positioning the mandrel entirely on the exit side of said die, and continuing pulling of said tube until the operation is completed. 